As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased as an energy source for the mobile devices. Among such secondary batteries is a lithium secondary battery having a high energy density and discharge voltage, into which much research has been carried out and which is now commercialized and widely used.
In general, a secondary battery is configured to have a structure in which an electrode stack including a positive electrode and a negative electrode stacked or wound in a state in which a separator is disposed between the positive electrode and the negative electrode is mounted in a battery case made of a metal or a laminate sheet, and an electrolyte is injected into the battery case or the electrode stack is impregnated with the electrolyte.
The secondary battery has problems in that the volume of the secondary battery is increased due to swelling of negative electrodes, on each of which an active material is coated, or generation of gas from the secondary battery during the use of the secondary battery, and an electrolyte in the secondary battery is gradually exhausted due to side reactions of the negative electrodes or oxidation of an electrolyte on positive electrodes, whereby the life span of the secondary battery is reduced.
In order to prevent such phenomena, it is important to restrain swelling of the electrodes in the secondary battery with appropriate pressure, thereby increasing efficiency of the secondary battery and thus improving performance of the secondary battery. Conventionally, however, it is not possible to pressurize the entirety of each of the electrodes at uniform pressure.
Therefore, there is a high necessity for a novel lithium secondary battery that is capable of solving the above problems.